An attack at a mosque in which three men and a police officer were stabbed is thought to have happened after one worshipper turned on others, MP Liam Byrne has said.
The incident happened at around 11pm last night at the mosque in the Ward End area of Birmingham.
A male police constable was injured when he arrived at the scene after responding to reports that three men had been stabbed.
Speaking at the scene today, which has been placed under police cordon, Mr Byrne, MP for Birmingham Hodge Hill, said: "The community and the police have pulled together really quickly since the incident last night.
"What is already clear is that this was not a hate crime - this was a tragic, sad, and isolated incident.
"What's really important now is that people stay very calm. We pray for those who've been hurt and rally round their families and we let justice now take its course.
"The police have somebody in custody and I think what we would want to say is that it's been brilliant how police and the community came together to contain the incident last night.
"And above all, we want to praise the courage of West Midlands Police, they will do anything and everything to keep people safe in this community."
Mr Byrne said it was his understanding that the man in police custody had been attending the mosque when the attack happened.
"What appears to have happened is that one worshipper turned on a number of other worshippers," Mr Byrne said.
"The police were there really quickly to help make sure that everyone there was safe and people pulled together to contain the situation."
A 32-year-old man is currently being questioned on suspicion of attempted murder, West Midlands Police said.
The four wounded men are described as being in a "stable" condition in hospital.
Local resident Madaser Hussain said the atmosphere in the community was unpleasant following the incident.
"There shouldn't be any bloodshed on the streets or anywhere," he said, "we should be one community, really."
He said he did not know anything about an argument between worshippers but saw people running out of the mosque last night.
"All I heard was loud noises and people screaming," he said.
"I live round here, I was walking and I went past and heard screams, as I was about to enter I saw people rushing out so I knew there was something wrong but I didn't go in to see what had happened.
"Men were running out and saying 'there's been people stabbed inside there'."
The mosque, called Washwood Heath Muslim Centre, had been sectioned off by police tape this morning.
Many people living locally stood out on the street to watch what was happening as police maintained a presence in the area.
A police spokeswoman said earlier: "Police were called at 11pm on Saturday night to a mosque in Washwood Heath Road, Ward End, to reports of three men with stab wounds.
"Officers arrived at the incident and whilst the man was being detained, one police officer also suffered a stab wound."
Mohammed Shafiq, the leader of national Muslim organisation the Ramadhan Foundation, said a nearby resident overheard an argument coming from inside the mosque and believes the attack followed a dispute between members.
"I have spoken to someone who lives a few doors down from the mosque and they described hearing an argument between some of the people inside the mosque," he said.
"It escalated into violence and a police officer has been stabbed.
"People, anti-Muslim extremists, are going to try to take advantage of this - it's very serious that a police officer has been stabbed during duty.
"The aftermath of the brutal murder of Lee Rigby has led to an increase of attacks.
"The involvement of a police officer in this incident obviously causes more concern."
He went on: "Our immediate thoughts are with the victims injured and their families.
"It is too early to speculate on the circumstances of the stabbings but we must be clear there should be no place for this sort of violence in our country.
"There will obviously be people who will try to take advantage of this tragedy but we must not allow them to succeed."
Police said earlier they were investigating whether the attack was a hate crime.
"We don't know at the moment, it's very early stages in the inquiry," the spokeswoman said.
"We can't rule anything out at the moment."
A number of mosques have been targeted since the brutal killing of Drummer Rigby close to his barracks in Woolwich, south London, last month.